Overvoltage protector

ABSTRACT

An overvoltage protector having a housing and at least one overvoltage limiter arranged in the housing, especially a gas-filled surge arrester ( 1 ), a suppressor diode ( 2 ) or a varistor. The functional ability and the state of the overvoltage protector can be controlled during operation by associating a monitoring component with the overvoltage limiter which detects a current (i) flowing over the overvoltage limiter component, and by providing an evaluation unit that evaluates the signal of the monitoring component.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of commonly owned, co-pending U.S. patentapplication Ser. No. 13/144,170, filed Jul. 12, 2011; claims the benefitof, and incorporates by reference, International Application No.PCT/EP2010/000041, filed on Jan. 7, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an overvoltage protector with a housing andwith at least one overvoltage limiter which is located in the housing,the overvoltage limiter being especially a gas-filled surge arrester, aspark gap, a suppressor diode or a varistor.

2. Description of Related Art

Overvoltage protection can be divided into different areas ofapplication. Here, it is distinguished between overvoltage protectionfor power supply, for measurement, open-loop and closed loop control(MSR) technology and for information technology and telecommunications.Interfaces of MSR technology are far more sensitive to overvoltages thanpower supply systems. For overvoltage protection, therefore, in the MSRdomain, generally, overvoltage protectors with combined protectivecircuits are used, at least one overvoltage limiter being used forcoarse protection and at least one overvoltage limiter being used forprecision protection. Often, an indirect parallel connection of agas-filled surge arrester and a suppressor diode is used, a decouplingresistor being located between the gas-filled surge arrester and thesuppressor diode.

The known overvoltage protectors are often made as “protective plugs”which form an overvoltage protection device together with the bottompart of the device. For installation of this overvoltage protectiondevice, there are corresponding terminals for the individual conductorson the bottom part of the device. For simple mechanical and electricalcontact-making of the bottom part of the device with the respectiveovervoltage protector, the connecting elements in the overvoltageprotector are made as plug pins for which there are correspondingsockets connected to the terminals in the bottom part of the device sothat the overvoltage protector can simply be slipped onto the lower partof the device.

In these overvoltage protection devices, the installation and mountingcan be done very easily in a time-saving manner due to the plug-incapacity of the overvoltage protector. In addition, these overvoltageprotectors partially have a remote reporting capability, as a primarydetector of the state of the overvoltage protector which isconventionally made as a changeover contact, and an optical statedisplay in the overvoltage protector. The state display indicateswhether the overvoltage limiter located in the overvoltage protector isstill serviceable or not. Depending on the application of theovervoltage protector, varistors, gas-filled surge arresters, sparkgasps or diodes, especially suppressor diodes, are used as overvoltagelimiter.

Due to ageing, prior damage by discharge processes and intermittentlyoccurring overvoltages (TOV) in the range of seconds, an unwantedincrease of the leakage current of the varistor at operating voltagesoccurs, especially in overvoltage protectors with a varistor as theovervoltage limiter. Therefore, overvoltage protectors with a varistoras arrester, at present, often have a thermal disconnect device by whicha varistor which is no longer reliably serviceable is electricallydisconnected from the current path which is to be monitored. Moreover,thermal disconnection devices are often also used in overvoltageprotectors with spark gaps as arresters.

Such an overvoltage protector is known, for example, from German PatentApplication DE 20 2004 006 227 U1. In the known overvoltage protector,the state of the overvoltage limiter, especially a varistor, ismonitored according to the principle of a temperature switch so that,when the varistor overheats, a solder connection provided between thevaristor and a disconnector is interrupted; this leads to electricaldisconnection of the varistor. Moreover, when the solder connection isinterrupted a plastic element is pushed by the reset force of a springout of a first position into a second position in which thedisconnector, which is made as an elastic metal tongue, is thermally andelectrically disconnected from the varistor by the plastic element.Since the plastic element has two colored markings which are locatednext to one another, it also acts in addition as an optical statedisplay, as a result of which the state of the overvoltage protector canbe easily read off directly on site. However only one defect of theovervoltage protector can be signaled by such an integrated display.

Since overvoltage protection devices are exposed to high peak currentloads, the individual overvoltage limiters can be damaged depending onthe level and frequency of the stresses so that the serviceability ofthe overvoltage elements should generally be monitored. To monitor theserviceability of plug-in overvoltage protectors, Phoenix Contact GmbH &Co. KG sells a portable arrester test device under the name“CHECKMASTER” (catalog TRABTECH 2007, pages 166 to 173) which has a testreceiver into which the protective plug which is to be tested at thetime can be plugged. In doing so, the current electrical parameters ofthe overvoltage limiters are determined and compared to referencevalues, by measuring the tolerance values highly loaded components beingidentified as damaged beforehand. The arrester test device thusenables—in addition to the display of a defective overvoltageprotector—also a precautionary examination of an overvoltage protector.But the disadvantage is that for this purpose the overvoltage protectormust be removed from the bottom part of the device so that a test is notpossible during operation.

SUMMARY OF THE INVENTION

Therefore, the object of this invention is to make available aovervoltage protector of the initially described type which enablesmonitoring of the serviceability and of the state of the overvoltageprotector during operation.

This object is achieved in the initially described overvoltage protectorin that a monitoring component is assigned to the overvoltage limiterand detects a current flowing via the overvoltage limiter and that thereis an evaluation unit which evaluates the signal of the monitoringcomponent.

Because a monitoring component is assigned to the overvoltage limiterand detects a current flowing via the overvoltage limiter, especially adischarge current, detection of the stress on the overvoltage limiter inoperation is possible. By using a corresponding evaluation unit whichevaluates the signal which has been delivered from the monitoringcomponent based on the current which is flowing via the overvoltagelimiter, a conclusion about the loading of an overvoltage limiter ispossible before a defect of the component occurs. Thus, overvoltageprotectors which have been damaged beforehand can be recognized andreplaced in time. The evaluation unit is preferably made such that, inaddition to the frequency and the level of the loading of an overvoltagelimiter, it also evaluates the duration of the loading, i.e., theduration of the discharge current.

According to one advantageous configuration of the invention, theevaluation unit is electrically isolated from the discharge current pathvia which the current which has been detected by the monitoringcomponent flows. Since, when there is an overvoltage a very high,current can flow via the overvoltage limiter, especially a gas-filledsurge arrester or a spark gap, the electrical isolation of theevaluation unit from the discharge current path protects the evaluationunit against damage and enables a reduction of the amplitude of thesignal which is to be evaluated by the evaluation unit.

In a first preferred version of the overvoltage protector in accordancewith the invention, the monitoring component is a coil which isinductively coupled to the discharge current path, the coil beingconnected to an integrator. By using a coil, the discharge current canbe detected without the actual protective relay, i.e., the dischargecurrent path, being influenced. By using an integrator, not only theintensity of the current pulse flowing through the coil as a result ofthe discharge current, but its energy are determined. From the pulseenergy which has been determined in this way the loads of theovervoltage limiter, especially of a gas-filled surge arrester, can bedetermined and evaluated, individually or added up.

In the simplest case, the integrator can be a capacitor which is chargedby the current which is flowing though the coil so that then the voltagevia the capacitor is evaluated. Alternatively, the integrator can alsobe a microcontroller with a preferably integrated analog-digitalconverter.

According to a second version of the overvoltage protector in accordancewith the invention, the monitoring component is a photoelement. In thisversion, the overvoltage limiter is a gas-filled surge arrester or aspark gap. For a gas-filled surge arrester or spark gap, when anovervoltage is present, an arc forms between the two electrodes viawhich the discharge current flows. The photoelement is opticallyconnected to the gas-filled surge arrester or the spark gap such thatthe photoelement detects the prevailing arc. Electrical isolationbetween the discharge current path and the evaluation unit which islocated downstream of the photoelement takes place by the photoelement.

The evaluation unit in this version of the overvoltage protector inaccordance with the invention is made such that, preferably, both theintensity and also the duration of the arc can be evaluated. Oneadvantage of this version consists especially in that, by evaluating theduration of the arc, it can be recognized if the arc is not extinguishedafter the actual discharge process; this results in that a line followcurrent unintentionally flows via the existing arc.

According to another version of the overvoltage protector in accordancewith the invention, the monitoring component is an optical coupler whichis connected in parallel to a resistor located in series with theovervoltage limiter and detects the current flowing through theresistor. The use of an optical coupler as a monitoring component issuitable both for overvoltage limiters which are used for coarseprotection, for example, for a gas-filled surge arrester or a spark gap,and also in overvoltage limiters which are used for precisionprotection, for example, a suppressor diode.

If the optical coupler is used for monitoring the operation of agas-filled surge arrester or a spark gap, the resistor which isseries-connected to the overvoltage limiter and which is connectedparallel to the optical coupler has the function of a shunt. Theresistor thus has a relatively low value so that it does not influencethe operation of the overvoltage limiter.

According to one preferred configuration of the third version in whichthe overvoltage protector has both a gas-filled surge arrester or aspark gap and also a suppressor diode as overvoltage limiters and inwhich there is a decoupling resistor between the gas-filled surgearrester or the spark gap and the suppressor diode, the optical coupleris connected parallel to the decoupling resistor. An overvoltageprotector with a gas-filled surge arrester, a suppressor diode and adecoupling resistor is known from the prior art, especially in the MSRdomain. To monitor the state of the suppressor diode, the opticalcoupler, as a monitoring component, is simply connected in parallel tothe decoupling resistor which is present anyway. For high-resistancetermination of the overvoltage protector, the current through thedecoupling resistor corresponds to the current through the suppressordiode so that, by detecting the current through the decoupling resistorusing the optical coupler, the loading of the suppressor diode isdetermined, and from it, a conclusion about its presumable service lifecan be drawn. Moreover, it can be recognized when the allowable loadcurrent flowing through the decoupling resistor is exceeded, so thatdamage of the resistor can be displayed and prevented.

Regardless of whether a gas-filled surge arrester or a suppressor diodeis being monitored for its operation by means of the optical coupler,the electrical isolation to the evaluation unit is established by theoptical coupler and converts a measured current through the dischargecurrent path into a smaller current which can be easily measured andevaluated. It is of course also possible that for an overvoltage elementwith a gas-filled surge arrester or a spark gap and with a suppressordiode the serviceability of the gas-filled surge arrester is monitoredby an optical coupler and the serviceability of the suppressor diode ismonitored by another optical coupler.

According to an alternative version of the invention, the aforementionedobject is achieved, in an overvoltage protector with a suppressor diodeas the voltage limiter, in that the suppressor diode is located in thebridge branch of a diode bridge circuit and that a capacitancemeasurement device is connected to the suppressor diode, the capacitancemeasurement device detecting the capacitance or capacitance change ofthe suppressor diode. The capacitance measurement device can be, forexample, an oscillator. The arrangement of the suppressor diode in thebridge branch of a diode bridge circuit enables measurement of thecapacitance or capacitance change of the suppressor diode without theoperation of the suppressor diode as an overvoltage limiter beinginfluenced. The change of the capacitance of the suppressor diode is anindication of a change of the suppressor diode and thus of completedloading of the suppressor diode.

Advantageously, the four diodes of the diode bridge circuit each have amuch lower capacitance than the suppressor diode. In this way, the totalcapacitance of the diode bridge circuit is reduced, as a result of whicha higher maximum signal frequency of the connected circuit is enabled.

According to one configuration of the overvoltage protector inaccordance with the invention which is advantageously implemented bothin the first alternative and also the second alternative, there is atleast one optical state display for at least one overvoltage limiter inthe housing so that the state of the overvoltage protector or of anovervoltage limiter can be displayed directly on site. The state displaycan preferably have three regions with different markings, especiallythree regions with different colors, for example, green, yellow and red,so that not only the defect of an overvoltage limiter, but prior damagecan be displayed. If the overvoltage protector has several overvoltagelimiters, for each limiter, its state can be separately displayed.

According to another advantageous configuration of the invention, theovervoltage protector in addition to the optical state display also hasa telecommunications contact for remote indication of the state of theovervoltage protector or of the states of the individual overvoltagelimiters.

In particular, there are now a host of possibilities for embodying anddeveloping the overvoltage protector in accordance with the invention.In this regard reference is made the following description of preferredexemplary embodiments in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified circuit diagram of a first version of anovervoltage protector in accordance with the invention,

FIG. 2 shows a simplified circuit diagram of a second version of anovervoltage protector in accordance with the invention,

FIG. 3 shows a simplified circuit diagram of a third version of anovervoltage protector in accordance with the invention,

FIG. 4 shows a simplified circuit diagram of a fourth version of anovervoltage protector in accordance with the invention,

FIG. 5 shows a simplified circuit diagram of another version of anovervoltage protector in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The figures each show a simplified circuit diagram of a respectiveversion of the overvoltage protector in accordance with the invention.In the circuit diagrams, only the overvoltage limiter or limiters and amonitoring component are shown. FIGS. 1 to 3 each show an exemplaryembodiment in which the overvoltage limiter is a gas-filled surgearrester 1. In the exemplary embodiments according to FIGS. 4 and 5, inaddition to a gas-filled surge arrester 1 for coarse protection, thereis also a suppressor diode 2 for precision protection. The simplifiedcircuits shown in the figures have two input terminals 3 for connectionof two lines and two output terminals 4 for connection of the device tobe protected, for example, a sensor or a control. There can be otherterminals, especially a ground terminal, even if they are not shown inthe figures.

It is common to the exemplary embodiments according to FIGS. 1 to 4 thata monitoring component is assigned to the gas-filled surge arrester 1(FIGS. 1 to 3) or the suppressor diode 2 (FIG. 4) which detects acurrent i flowing via the gas-filled surge arrester 1 or the suppressordiode 2. The signal which is generated depending on the current i fromthe monitoring component is evaluated in an evaluation unit (not shownhere), the evaluation unit in the exemplary embodiments according toFIGS. 1 to 4 being electrically isolated from the discharge current path5 via which the current i flows through the gas-filled surge arrester 1or the suppressor diode 2.

In the exemplary embodiment according to FIG. 1, the monitoringcomponent is a coil 6 which is inductively coupled to the discharge path5 so that a current i from the coil 6 is detected by the gas-filledsurge arrester 1. The coil 6 is connected to an integrator 7, as aresult of which the energy of the current pulse can be determined by thegas-filled surge arrester 1. The loading of the gas-filled surgearrester 1 by the discharge current i can be determined from the pulseenergy.

In the exemplary embodiment according to FIG. 2, a photoelement 8 isused as a monitoring component, the photoelement 8 being locatedadjacent to the gas-filled surge arrester 1 such that an arc whichprevails in the gas-filled surge arrester 1 when an overvoltage ispresent is detected by the photoelement 8. Suitable signal processingmakes it possible to determine the intensity and the duration of thedischarge process using the arc which has been detected by thephotoelement 8, and thus, provides a measure of the loading of thegas-filled surge arrester 1.

In the two embodiments according to FIGS. 3 and 4, the monitoringcomponent is an optical coupler 9, the optical coupler 9 in the versionaccording to FIG. 3 being parallel to a resistor 10 which is in serieswith the gas-filled surge arrester 1. While in the exemplary embodimentaccording to FIG. 3 the serviceability of the gas-filled surge arrester1 is monitored with the optical coupler 9, the optical coupler 9 in theexemplary embodiment according to FIG. 4 is used for monitoring of thesuppressor diode 2. For this purpose, the optical coupler 9 is connectedin parallel to a decoupling resistor 11 which is located between thegas-filled surge arrester 1 and the suppressor diode 2.

In the current path of the optical coupler 9, there is another resistor12 whose resistance value is much larger than the resistance value ofthe resistor 10 or of the decoupling resistor 11. In the exemplaryembodiment according to FIG. 4, the decoupling resistor 11 is in therange of a few ohms while the resistor 12 is, for example, in the rangeof a few hundred ohms.

The optical coupler 9 is used to detect the current flowing through theresistor 10 or the decoupling resistor 11, with the optical coupler 9 ora downstream evaluation unit both the amplitude and also the duration ofa current pulse i being detected which is flowing through the resistor10 or the decoupling resistor 11, and thus, for a high-resistancetermination also through the gas-filled surge arrester 1 and thesuppressor diode 2.

FIG. 5 shows a version of an overvoltage protector with a gas-filledsurge arrester 1 and a suppressor diode 2 in which the state of thesuppressor diode 2 is checked by the capacitance C_(x) and a capacitancechange of the suppressor diode 2 is detected, for which a capacitancemeasurement device 13, for example, an oscillator and/or amicrocontroller, is connected to the suppressor diode 2. As is apparentfrom FIG. 5, the suppressor diode 2 is in the bridge branch 14 of adiode bridge circuit 15 which has four diodes, as a result of which thecapacitance C_(x) can be measured without the operation of thesuppressor diode 2 as an overvoltage limiter, specifically as precisionprotection of the overvoltage protector, being influenced. Theindividual diodes of the diode bridge circuit 15 have a much smallercapacitance than the suppressor diode 2.

Even if, in FIGS. 1 to 5, there is only one monitoring component formonitoring the serviceability of a respective overvoltage limiter, it isapparent to one skilled in the art that, to monitor several overvoltagelimiters, there can also be several identical or different monitoringcomponents.

Thus, for example, in an overvoltage protector according to FIG. 4 whichhas both a gas-filled surge arrester 1 and also a suppressor diode 2,the serviceability of the gas-filled surge arrester 1 is monitored bymeans of a first optical coupler 9 and the serviceability of thesuppressor diode 2 is monitored by means of a second optical coupler 9.It is likewise also possible, for example, to monitor the serviceabilityof the gas-filled surge arrester 1 with a coil 6 according to FIG. 1 orwith a photoelement 8 according to FIG. 2 in the overvoltage protectorsshown in FIGS. 4 and 5.

What is claimed is:
 1. Overvoltage protector, comprising: a housing andat least one suppressor diode which is located in the housing as anovervoltage limiter, wherein a suppressor diode is located in a bridgebranch of a diode bridge circuit and wherein a capacitance measurementdevice is connected to the suppressor diode, the capacitance measurementdevice being adapted for detecting a capacitance or capacitance changeof the suppressor diode.
 2. Overvoltage protector as claimed in claim 1,wherein the capacitance measurement device is at least one of anoscillator and a microcontroller.
 3. Overvoltage protector as claimed inclaim 1, wherein the diodes of the diode bridge circuit each have asmaller capacitance than that of the suppressor diode.
 4. Overvoltageprotector as claimed in claim 1, wherein an optical state display for atleast one overvoltage limiter is located in the housing.
 5. Overvoltageprotector as claimed in claim 1, wherein a telecommunications contactfor remote indication of the state of at least one overvoltage limiteris located in the housing.